A typical sprinkler system for fire protection is connected to a water supply (city supply, gravity tank or pump) and includes a system riser pipe that feeds a main pipe, a system valve that is typically located in the riser pipe, cross main pipes that receive water from the main pipe and feed branch lines, branch lines, sprinklers mounted in the branch lines, and other accessories. In a conventional wet-pipe sprinkler system, water is discharged under pressure as soon as the first sprinkler directly above a fire is actuated, or as soon as the first few sprinklers directly above a fire are actuated. Additional sprinklers will not be actuated until the fire grows further and overpowers the sprinkler or sprinklers that are already operating.
Control-mode wet-pipe fire sprinkler protection systems use ceiling sprinklers that are equipped with thermal sensing elements, typically fusible links or glass bulbs, and, prior to the fire protection sprinkler systems disclosed in co-pending U.S. application Ser. No. 11/370,904 of Hong-Zeng Yu, filed on Mar. 9, 2006, had high temperature ratings and low thermal sensitivity. The low thermal sensitivity means that the thermal sensing elements had high Response-Time-Index (RTI) values. Response-Time-Index indicates how fast a sprinkler can absorb, from its surroundings, heat sufficient to cause actuation.
As a result of the high Response-Time-Index values, the control-mode wet-pipe systems in general actuated relatively slowly and had to fight against fires that were already large when water began to discharge from actuated sprinklers. As the fire challenge increased, more and more water droplets tended to be deflected by the fire plume back up to the ceiling level and carried laterally in the ceiling gas flow. Water droplets present in the ceiling gas flow can impact, wet and cool the thermal sensing elements of sprinklers adjacent to the operating sprinklers and, thus, cause temporary or permanent delay of the actuation of these adjacent sprinklers, which are close to the fire, while sprinklers that are farther from the fire and have unwetted thermal sensing elements are actuated.
The aforementioned temporary or permanent delay of sprinkler actuations is known as sprinkler skipping. For wet-pipe sprinkler systems known before those of Ser. No. 11/370,904, sprinkler skipping could be caused by one or more sprinklers discharging water as soon as they are actuated by the fire. As a result, the water spray coverage area varied with time and could consist of dry spots or low water-flux spots in the protected area. Consequently, the fire continued to spread, and the effectiveness of the sprinkler protection was severely reduced.
In fire protection sprinkler systems disclosed in Ser. No. 11/370,904, which is incorporated herein by reference in its entirety, water is not discharged from any sprinklers until all of the sprinklers in a designated area above the fire are actuated. By “actuated” is meant that a sprinkler is opened, not necessarily that water or another extinguishant flows under operating pressure through the sprinkler. By “designated area” is meant the area directly above a fire, so that water discharged from the actuated sprinklers in the designated area covers the fire. In sprinkler systems disclosed in Ser. No. 11/370,904, the sprinklers in the designated area actuate progressively in all radial directions from the fire origin without skipping, because no water is discharged until all the sprinklers in the designated area above the fire are actuated. Then, water is discharged simultaneously from all the actuated sprinklers. As a result, the fire is completely covered and surrounded by the sprinkler sprays, with no dry spots, and the effectiveness of the sprinkler system does not suffer due to sprinkler skipping. Sprinkler skipping is pre-empted by deluging the fire with closed-head type sprinklers, including conventional sprinklers and spray sprinklers.
The sprinkler systems disclosed in Ser. No. 11/370,904 are in contrast to sprinkler systems commonly called “deluge” sprinkler systems. In “deluge” sprinkler systems, the sprinklers have no thermal sensing elements, such as fusible links or glass bulbs, but instead are always open to allow water to flow out freely from all of the sprinklers. A system valve that is opened by a fire detector is provided in “deluge” sprinkler systems upstream of all of the sprinklers. The sprinkler systems disclosed in Ser. No. 11/370,904 enable sprinklers having thermal sensing elements to produce a deluge of water through all of the sprinklers in the designated area all at once, thereby suppressing the fire, even though the thermal sensing elements keep the sprinklers closed until actuation. As a result, no or few additional sprinklers are needed to be actuated beyond the designated area.
In order to cover the fire hazards in most industrial occupancies, the sprinkler systems disclosed in Ser. No. 11/370,904 overcome the problem of sprinkler skipping by assuring that all of the sprinklers in the designated area actuate more quickly than in known systems and at the same time as one another. The sprinklers have an RTI value and a temperature rating such that the combination of the RTI value and the temperature rating prevents the sprinklers that are outside a designated area directly above the fire from actuating before extinguishant that is under the pressure of a source is discharged from any of the sprinklers of the sprinkler system. Extinguishant does not flow out of any of the sprinklers instantaneously. Instead, the RTI and the temperature rating are chosen such that the thermal elements of a group of sprinklers in the designated area actuate before extinguishant under the operating pressure is discharged from any of the sprinklers. Nevertheless, the extinguishant in the system begins discharging under pressure from the actuated sprinklers fast, that is, faster than in conventional dry-pipe systems. Since the pattern of ceiling gas flow induced by a fire plume is close to being axi-symmetrical, and since the arrangement of sprinklers in a sprinkler system is typically in square or rectangular pattern, the area in which sprinklers actuate tends to have a pattern of between circular and square or between circular and rectangular. The system valve, which is positioned upstream of all of the sprinklers in the system, is timed to open after or shortly before all of the sprinklers exposed to the fire have actuated, so that sprinklers discharge at the designated operating pressure shortly after all the sprinklers in the designated area are actuated.
One of the essential elements for the deluge-like wet-pipe sprinkler system is a system valve which is capable of activating timely so that the actuated sprinklers will discharge at the operating pressure at or shortly after the time when all the sprinklers in the intended spray coverage area are actuated.
Since the sprinkler pipes are filled with water, or other liquid extinguishant, for wet-pipe applications, the time delay for extinguishant pressure to reach the designated operating pressure is estimated to be less than five seconds after the system valve is activated where the extinguishant comes from a typical water supply required for warehouse protection. Because of the small time delay, the system valve should activate around the time when all or most of the sprinklers in the designated area are actuated, depending on the actual time delay.
U.S. Pat. No. 5,511,621 to Yao discloses a dry-pipe sprinkler system in which the discharge of water from nozzles over a fire is delayed until one or two rings of nozzles around the fire actuate.